This invention concerns a weaving machine, in particular a weaving machine with a lock.
It is known for weaving machines that the harness motion can be obtained by means of a positive or negative drive. A negative drive moves the harness frames in one direction through cams, and in the other direction through springs which ensure the contact with the cams. The harness drive is coupled to the main shaft of the weaving machine.
It is also known that the main shaft of the weaving machine can be equipped with an electromagnetic brake, which is activated by electric energization. When the weaving machine stops, this brake is energized. In the case of weaving machines with a negative harness drive, it is clear that the brake must also receive a couple at standstill, namely the couple exercised by the springs of the harness frames on the harness drive and therefore also on the main shaft. The intensity and direction of this couple depend of course on the position of the main shaft and the position of the various harnesses.
If in such a weaving machine a voltage failure occurs in the power supply of the electromagnetic brake, the brake couple is eliminated and the harness frames are moved by the above-mentioned springs until a state of equilibrium has been reached. The main shaft and the sley are hereby also moved. It is clear that this is very dangerous for a weaver working on the weaving machine, particularly when pulling a new warp thread through the reed and through the harnesses, when repairing a weft thread in the shed and when regulating the gripper course on gripper weaving machines.
In order to reduce the above-mentioned risk, said weaving machines are usually equipped with capacitors which ensure the energization of the electromagnetic brake for a period of time after the mains voltage has failed. This period is usually insufficient to do normal repair work on a weft thread or warp thread.
For other repair work which can take a long time, such as the maintenance of the weaving machine, the brake is previously uncoupled, so that a state of equilibrium is reached. The disadvantage is, however, that at the start of the weaving machine, the various weaving machine parts are not any longer in their optimum position to avoid starting marks and the like.
According to another possibility, in case of longer standstills of the weaving machine the springs of the harness frames can be uncoupled. However, this is a relatively cumbersome job.
According to another known possibility, an electromagnetic brake is used, whereby the brake force is obtained under the influence of a spring force, and whereby the deactivation of this brake is done by energizing the electromagnet, such that the brake is opened against the spring force. This brake has the disadvantage that a large amount of energy is required during the normal operation of the weaving machine. Such a brake also has the disadvantage that, during a standstill, the weaving machine is entirely blocked and that a rotation by means of the hand wheel is no longer possible, unless a special device is provided with the aim of deactivating this brake manually.
Apparently, the above-mentioned problem occurs less frequently on weaving machines with a positive harness drive. In such a positive harness drive, the movement of the harness frames in both directions is exclusively obtained by means of cam guides. When the weaving machine stops, a considerable couple may occur when the largest number of harnesses are in their highest position, while only a few harness frames are in their lowest position. Indeed, in that case it is possible that the weaving machine is set in motion due to the weight of the lifted harness frames or due to the tension in the warp threads.
However, the above-mentioned problem can also occur in other cases than with a negative harness drive, for instance on weaving machines whereby the sley or another weaving machine part is charged by the springs in its retired position.